Disposal of crankcase fumes from diesel engines can be an environmental problem, particularly with engines used in marine applications. The fumes are produced due to blowby gas escaping past piston rings due to high pressure on fuel and air during compression and combustion. The blowby gas enters the engine crankcase where it picks up oil so the fumes include the blowby gas and an oil mist. In many applications, the fumes are merely released to the atmosphere which can cause undesirable oil deposits.
In marine applications, where avoidance of the emissions has been mandated by regulations, a practice has been to introduce the fumes into the engine air intake along with fresh air for consumption by the engine. That is adverse to the effective life of the air filter. Also, as the fumes pass through a typical engine system, including a turbocharger compressor, the compressor wheel becomes coated with oil deposits. This results in loss of compressor efficiency which leads to other problems with engine aspiration and smoke.
It has been recognized that it would be desirable to separate the oil from the rest of the fumes (generally referred to as "air" but containing gases that may include fuel vapor in addition to ambient air) prior to reintroducing the fumes back into the engine. Known separators proposed for this purpose either use induction air to coalesce the hot oil vapor into liquid or have a stationary filter with a diaphragm/valve assembly to regulate pressure.